Photometers are now being built which are capable of measuring multifunctions, i.e., they measure not only the absorbance of light by a sample material, but also they are able to make fluorescence, turbidimetric and nephelometric measurements. A photometer of this type is described in an application Ser. No. 731,781, entitled Absorbance, Turbidimetric, Fluorescence, and Nephelometric Photometer (Bach and Robertson) filed concurrently herewith. When making such multiple measurements, the light intensities impinging upon the photodetectors vary over a relatively large dynamic range. For example, when an array detector is used, the various photodiodes comprising the array detector may receive anything varying from a brief flash of fluorescence of relatively low intensity to a continuous relatively high intensity radiation such as provided by the output of an absorbance type measurement.
Another problem encountered with fluorescent measurements is that the light sources used for such measurements, typically a xenon tube, are relatively unsteady. Self interrogating integrating detectors are available for such measurements, but all of these are relatively expensive particularly since a separate channel must be used for each element of the array detector. As an alternative, multiplexing techniques may be used to pass the output of each element of an array detector to a single amplifier. Unfortunately, such approaches using multiplexers typically are more noisy and tend to be less suitable for low intensity light.